Method and Apparatus for Block-based Significance Map and Significance Group Flag Context Selection

Abstract

A method of significance group flag coding is disclosed. The method includes: receiving one or more significance group flags associated with a TU (transform unit), wherein the TU is divided into one or more sub-blocks; and coding said one or more significance group flags based on context set selection, wherein the context set selection is associated with significance map coding of the sub-block, and the context set selection depends on horizontal sub-block index, vertical sub-block index, or both the horizontal sub-block index and the vertical sub-block index.

1 . A method of significance group flag coding, the method comprising:
 receiving one or more significance group flags associated with a TU (transform unit), wherein the TU is divided into one or more sub-blocks; and   coding said one or more significance group flags based on context set selection, wherein the context set selection is associated with significance map coding of the sub-block, and the context set selection depends on horizontal sub-block index, vertical sub-block index, or both the horizontal sub-block index and the vertical sub-block index.   
     
     
         2 . The method of  claim 1 , wherein two sub-blocks use same second context selection, second context set selection, or second context formation selection for significance group flag coding if said two sub-blocks use same context selection, context set selection, or context formation selection for the significance map coding. 
     
     
         3 . The method of  claim 2 , wherein said same context, context set, or context formation for the significance map coding is determined by comparing the horizontal sub-block index, the vertical sub-block index, or a combination thereof with a threshold. 
     
     
         4 . The method of  claim 3 , wherein the threshold is related to a TU width, a TU height or a combination thereof. 
     
     
         5 . The method of  claim 4 , wherein the threshold is derived based on maximum of the TU width and the TU height divided by 16. 
     
     
         6 . The method of  claim 2 , wherein a sum of the horizontal sub-block index and the vertical sub-block index of each sub-block is used to classify each sub-block into a class, wherein said same second context, second context set, or second context formation is determined according to the class. 
     
     
         7 . The method of  claim 6 , wherein the sum is compared with a threshold to classify said each sub-block and the threshold is derived based on maximum of a TU width and a TU height divided by 16. 
     
     
         8 . The method of  claim 1 , wherein the sub-block has a size corresponding to a 4×4, 4×8, 8×4, 8×8, 16×16, or 32×32. 
     
     
         9 . An apparatus of significance group flag coding, the apparatus comprising one or more electronics circuits configured for:
 receiving one or more significance group flags associated with a TU (transform unit), wherein the TU is divided into one or more sub-blocks; and   coding said one or more significance group flags based on context set selection, wherein the context set selection is associated with significance map coding of the sub-block, and the context set selection depends on horizontal sub-block index, vertical sub-block index, or both the horizontal sub-block index and the vertical sub-block index.   
     
     
         10 . The apparatus of  claim 9 , wherein two sub-blocks use same second context selection, second context set selection, or second context formation selection for significance group flag coding if said two sub-blocks use same context selection, context set selection, or context formation selection for the significance map coding. 
     
     
         11 . The apparatus of  claim 10 , wherein said same context, context set, or context formation for the significance map coding is determined by comparing the horizontal sub-block index, the vertical sub-block index, or a combination thereof with a threshold. 
     
     
         12 . The apparatus of  claim 11 , wherein the threshold is related to a TU width, a TU height or a combination thereof. 
     
     
         13 . The apparatus of  claim 12 , wherein the threshold is derived based on maximum of the TU width and the TU height divided by 16. 
     
     
         14 . The apparatus of  claim 10 , wherein a sum of the horizontal sub-block index and the vertical sub-block index of each sub-block is used to classify each sub-block into a class, wherein said same second context, second context set, or second context formation is determined according to the class. 
     
     
         15 . The apparatus of  claim 14 , wherein the sum is compared with a threshold to classify said each sub-block and the threshold is derived based on maximum of a TU width and a TU height divided by 16. 
     
     
         16 . The apparatus of  claim 9 , wherein the sub-block has a size corresponding to a 4×4, 4×8, 8×4, 8×8, 16×16, or 32×32.